The present invention relates to an electrophotosensitive material containing a quinone derivative having an excellent electric charge transferability, which is used in image forming apparatuses such as electrostatic copying machine, facsimile and laser beam printer.
In the image forming apparatuses, a so-called organic photosensitive material has widely been used, which comprises an electric charge generating material generating an electric charge under light radiation, an electric charge transferring material transferring thus generated electric charge and a binder resin constituting a layer in which the above substances are dispersed.
The organic photosensitive material is divided into tow main classes of a single-layer type photosensitive material wherein an electric charge generating material and an electric charge transferring material are dispersed in the same photosensitive layer and a multi-layer type photosensitive material having a laminated structure of an electric charge generating layer containing an electric charge generating material and an electric charge transferring layer containing an electric charge transferring material. Further, in the multi-layer type photosensitive material, the electric charge transferring layer having a film thickness larger than that of the charge generating layer is deposited at the outermost layer of the photosensitive material in view of the mechanical strength.
The electric charge transferring material used in these photosensitive materials includes a hole transferability type one and an electron transferability type one, and among the electric charge transferring materials known until now almost all of electric charge transferring materials having high carrier mobility so as to provide practically useful sensitivity with the photosensitive material have hole transferability. Therefore, in the organic photosensitive material which is now put into practical use, the multi-layer type photosensitive material comprises the electric charge transferring layer at the outermost layer becomes a negatively charging type one inevitably.
However, this negatively charging type organic photosensitive material must be charged by negative corona charge accompanied with the generation of a large amount of ozone, thereby to cause problems such as influence on the environment and deterioration of the photosensitive material itself.
To solve the problems described above, it has been studied to use an electron transferring material as the electric charge transferring material.
Japanese Published Unexamined Patent Application (Kokai Tokkyo Koho Hei) No. 1-206349 suggests to use, as the electron transferring material, a compound having a structure of diphenoquinone or benzoquinone.
However, a compound having diphenoquinone structure or benzoquinone structure is poor in matching with the electric charge generating material and insufficient in injection of electrons into the electron transferring material from the electric charge generating material. Since such an electron transferring material has low compatibility with a binder resin and is not uniformly dispersed in a photosensitive layer, the hopping distance of electrons becomes longer and electrons are less likely to move at low electric field.
Accordingly, as is apparent from electrical characteristics test described in Examples described hereinafter, the above-described conventional photosensitive material containing an electron transferring material had problems such as high residual potential and poor sensitivity.
The single-layer photosensitive material has advantages that one photosensitive material can be used in both of positively and negatively charging type apparatuses by using electron and hole transferring materials in combination. However, there arise problems that, when using diphenoquinone derivative as the electron transferring material, a charge transfer complex is formed by an interaction between the electron and hole transferring materials, thereby inhibiting transfer of electrons and holes.
To solve the problems described above, Japanese Published Unexamined Patent Application (Kokai Tokkyo Koho Hei) Nos.7-261419 and 9-151157 disclose to use a naphtoquinone derivative as the electron transferring material.
However, even when using a naphthoquinone derivative as the electron transferring material, it is not sufficient in matching with the electron generating material and in compatibility with a binder resin.
Thus, an object of the present invention is to solve the technical problems described above and to provide an electrophotosensitive material whose sensitivity has been improved as compared with a conventional one.
While studying intensively to solve the problems described above, the present inventors have found a new fact that: a quinone derivative represented by the general formula (1): 
wherein R1 and R2 are the same or different and represent an alkyl group, R3 represents an alkyl group, an alkoxy group, an aryl group, an aralkyl group, a hydrogen atom or a halogen atom, R4 and R5 are the same or different and represent an alkyl group, an alkoxy group, an aryl group, an aralkyl group, a hydrogen atom or a halogen atom, or form a ring by binding each other, and m represents an integer of 1 to 4, and/or, a quinone derivative represented by the general formula (2): 
wherein R6 and R7 are the same or different and represent an alkyl group, R8 represents an alkyl group, an alkoxy group, an aryl group, an aralkyl group, a hydrogen atom or a halogen atom, X represents a halogen atom, and n and p represent an integer of 1 to 4, have higher electron transferability as compared with a conventional electron transferring material such as a compound having diphenoquinone structure or benzoquinone structure and an excellent compatibility with a binder resin. Quinone derivatives of the general formulas (1) and (2) are known compounds described in Tetrahedron Letters, Vol.24, No.34, pp3567-3570, 1983.
Thus, the present invention includes the following inventions.
1) An electrophotosensitive material comprising a conductive substrate and a photosensitive layer formed on the conductive substrate, the photosensitive layer containing a quinone derivative represented by the general formula (1) and/or a quinone derivative represented by the general formula (2).
2) The electrophotosensitive material according to the above item 1), wherein said photosensitive layer contains an electron acceptor.
3) The electrophotosensitive material according to the above item 1), wherein said photosensitive layer is a single layer constituent containing a binder resin, an electric charge generating material and a quinone derivative represented by the general formula (1) and/or a quinone derivative represented by the general formula (2) as an electron transferring material.
4) The electrophotosensitive material according to the above item 1), wherein said photosensitive layer is a multi layer constituent comprising an electric charge generating layer containing an electric charge generating material and an electric charge transferring layer containing a binder resin and a quinone derivative represented by the general formula (1) and/or a quinone derivative represented by the general formula (2) as an electron transferring material.
Quinone derivatives represented by the general formulas (1) and (2) [hereinafter, sometimes referred to as quinone derivative (1) and quinone derivative (2), and xe2x80x9cquinone derivativesxe2x80x9d is used as representing both (1) and (2).] have an excellent electron acceptability and further good compatibility with a binder resin, thereby making it possible to uniformly disperse in the binder resin. Furthermore, quinone derivatives (1) and (2) are superior in matching with the electric charge generating material and injection of electrons from the electric charge generating material is smoothly conducted. Accordingly, quinone derivatives (1) and (2) exhibit excellent electric charge transferability even at low electric field and are suited for use as the electron transferring material in the electrophotosensitive material.
Moreover, since quinone derivatives (1) and (2) do not form a charge transfer complex with the hole transferring material, they are used particularly preferably in the single-layer type photosensitive layer using the electron transferring material in combination with the hole transferring material.
The electrophotosensitive material of the present invention is characterized in that the photosensitive layer is formed on the conductive substrate and said photosensitive layer contains quinone derivative (1) and/or quinone derivative (2).
Since such electrophotosensitive material contains quinone derivative (1) and/or quinine derivative (2) which have excellent properties as described above in the photosensitive layer, the residual potential is lower and the sensitivity is higher as compared with those of the electrophotosensitive material containing conventional electron transferring material.
Thus, the photosensitive layer containing quinone derivative (1) and/or quinone derivative (2) is superior in electron transferability at low electric field and less likely to cause recombination ratio of electrons and holes in the photosensitive, whereby apparent electric charge generation efficiency approaches an actual value. As a result, the sensitivity of the photosensitive material containing such photosensitive layer is improved. The residual potential of the photosensitive material is also lowered, thereby improving the stability and durability on repeated exposure.
Accordingly, a positively charged type photosensitive material having a higer senisitivity as compared with conventional one can be obtained by using quinone derivative (1) and/or quinone derivative (2) as an electric charge generating material which is contained in an electric charge transferring layer of multi-layer type photosensitive material or as an electron transferring material which is contained in an photosensitive layer of single-layer type photosensitive material.
Since quinone derivatives (1) and (2) do not form a charge transfer complex with the hole transferring material as described above, a photosensitive material having higher sensitivity can be obtained when using them in a single-layer type photosensitive material containing the electron transferring material and hole transferring material in the same photosensitive layer.
In the electrophotosensitive material of single-layer type, quinone derivative (1) and /or quinone derivative is usually incorporated in the amount within from 5 to 500 parts by weight, preferably from 10 to 500 parts by weight, and more preferably from 10 to 80 parts by weight, based on 100 parts by weight of the binder resin.
In case that quinone derivatives (1) and/or (2) is in the amount of less than 5 parts by weight, the residual potential becomes higher thereby it is feared that the sensitivity becomes insufficient; in case the amount of more than 500 parts by weight, thereby making quinone derivatives (1) and/or (2) possible to crystallize and the electrophotosensitive material does not sufficiently exhibit its function.
In the electrophotosensitive material of the multi-layer type, it comprises an electric charge generating layer containing an electric charge generating material and an resin binder and a electric charge transferring layer containing quinone derivatives (1) and/or (2). In the multi-layer type one, quinone derivatives (1) and/or (2) is preferably incorporated in the amount within a range from 10 to 500 parts by weight, and more preferably from 25 to 100 parts by weight, according to the same reason in the single-layer type one.
Moreover, in case that an electric acceptor is incorporated in said photo sensitive layer, since the electron transferability is improved much further, the photosensitive material having higher sensitivity can be obtained.